Electronic switch with means to halt the flow of electrons to initiate an arc discharge



R. CREVELING CH WITH MEANS TO HALT THE FLOW ELECTRONIC SWIT ELEC'IRONS TO INITIATE AN ARC DISCHARGE Filed March 16, 1964 2 Sheets-Sheet l TRIGGER v NEGATIVE .Zizrazztar Robe/v Creve/ing United States Patent 3,317 787 ELECTRONIC SWITCH WITH MEANS T0 HALT THE FLOW 0F ELECTRONS T0 INITIATE AN ARC DISCHARGE Robert Creveling, 1415 Park Ave. SW., Albuquerque, N. Mex. 87104 Filed Mar. 16, 1964, Ser. No. 351,945 17 Claims. (Cl. 315-168) My invention relates generally to gaseous discharge devices, and more particularly to the cold-cathode type.

This type of device is commonly used where it is desired to hold off a high voltage until a specified time, at which time a trigger voltage is applied, allowing ionization of an atmosphere Within the device, and consequent conduction of electrical current through the ionized atmosphere. In particular, a cold-cathode device is used in applications where comparatively large amounts of power, necessary for operating heaters in hot-cathode devices, are not available or desirable. Previous coldcathode switches have been rather slow starting, have required trigger signals several kilovolts in amplitude, have been operable only at very high anode voltages, have required special materials for their cathodes and other electrodes, and have been relatively fragile.

Therefore it is a general object of my invention to provide a new and improved electronic switch which is operable over a wide range of anode voltages at high peak currents, which is considerably simpler, more rugged and easier to construct than those of the prior art, and which can be fired very quickly and precisely with a relatively small amount of trigger energy. Since my invention is a cold-cathode type of device, no cathode heater power is required.

Briefly, by invention accomplishes these and other objects which shall become apparent by means of a plurality of electrodes mounted within an ionizable atmosphere. A perforated electrode, which sometimes acts as a cathode, is spaced from the anode by a distance such that the product of said distance and the pressure of the atmosphere is represented by points on the Paschen curve for the atmosphere to the left of the lowermost portion of the curve. This spacing enables hold-off of extremely high voltages, the holdofif being even further increased by provision of a DC. glow discharge on the side of the perforated electrode opposite the anode side, the discharge being in a direction with electron flow away from the perforated electrode and away from the anode. When it is desired to fire the switch, the glow discharge is halted, so that the electrons cease to flow away from the perforated electrode and are hence attracted to the anode through the perforations. This action provides sufiicient electrodes to initiate an arc discharge within the atmosphere.

A better understanding of my invention may be had by reading the more detailed description to follow, in conjunction with the appended claims and the attached drawing, in which:

FIG. 1 is a longitudinal sectional view of a preferred embodiment of my invention, including suggested auxiliary circuitry;

FIG. 2 is a cross sectional view of the embodiment of FIG. 1, taken along the line 2-2;

FIG. 3 is a longitudinal sectional view of an alternate embodiment, with circuitry;

FIG. 4 is a plan view of a first perforated electrode in the embodiment of FIG. 3;

FIG. 5 is a plan view of a second perforated electrode in the embodiment of FIG. 3;

FIG. 6 shows graphically test data from the preferred embodiment; and

FIG. 7 is a waveform of anode current for the preferred embodiment at the time of firing.

Referring now to FIGS. 1 and 2, ceramic body 10 acts as an insulating enclosure for an ionizable atmosphere 11. Planar anode 12 has a generally T-shaped longitudinal section including hollow portion 13, the interior of which contains part of atmosphere 11 and which is connected to the remainder of the atmosphere by center perforation 14. The upper end of hollow portion 13 is seen to be pinched off, this furnishing the final seal after the suitable atmosphere is forced in at the desired pressure.

Perforated solid electrode 20 may be made of any metal, and is brazed at its junctions with ceramic body 10 to form a gas-tight seal. The electrode is seen to be radially slotted at 21, for example, for reasons later to be explained. A second perforated electrode 22 is identical with electrode 20 and is spaced therefrom'by a considerably greater distance than the distance between electrode 20 and anode 12. A third electrode 23 covers the other end of ceramic body 10, and is brazed thereto.

The circuitry necessary for firing my electronic switch is simple. A high voltage is furnished by battery 25 or other source, and is transmitted to portion 13 of anode 12 and to capacitor 28 through resistor 26. Load'27, through which it is desired to conduct a sudden heavy capacitive discharge current upon firing of the switch, is connected between capacitor 28, and ground. Perforated electrode 20 also is grounded, while electrode 23 is connected to the high voltage by means of, resistor '29 When it is desired to fire the switch a negative trigger is furnished from source 30 through capacitor 31 to perforated electrode 22.

It has long been known that the voltage necessary to cause ionization between planar parallel electrodes is a function of the product of electrode separation and the pressure of the atmosphere between the electrodes. Curves of the breakdown voltage ordinate versus pressure times separation distance (pd) abscissa" are called Paschen curves. Such curves have a characteristic shape, rising generally to the left from a lowermost portion, thus indicating that the breakdown voltage increases as the product of separation and presesure decreases. I

The spacing between anode 12 and electrode 20 in my invention is chosen, along with the pressure of the atmosphere within the ceramic body, so that operation will be somewhere on the left hand side of the Paschen curve. Spacing between electrodes20 and 22, and betweenelectrodes 22 and 23, is considerably greater so that operation will be near the bottom or even on the right hand portion of the Paschen curve, meaning that breakdown will occur between these electrodes at a considerably lower voltage than that required to break down the atmosphere between the anode and electrode 20. With the circuitry shown in FIG. 1, then, assuming suitable values for resistors 26 and 29, there will be no breakdown and hence no large conduction between anode 12 and electrode 2%. However, there will be breakdown and conduction between electrode 23 and electrode 20. Resistor 29 limits this conduction preferably in the normal giow region. Electron flow will be from electrode 20 through the radial slots in electrode 22 to electrode 23 acting as a cathode during this normal glow discharge. There will be a very small flow of electrons from electrode 29 through its slots 21 to anode 12. However, the quantity of electrons is insufficient to cause breakdown between electrode 20 and anode 12. The few electrons which do penetrate the slots into the anodecathode region are swept away with any ions that may be produced. These are removed expeditiously, as are the ions and electrons associated with the dark current in the region.

Since a very high potential is applied between anode 12 and electrode 20, a very strong electric field exists between them. In the absence of a normal glow discharge on the other side of electrode 20, the tendency of this electric field would be to protrude through slots 21. This would mean that a stray electron following the electric field could travel a rather long path, considerably longer than the spacing between anode 12 and electrode 20, and perhaps sufficiently long so that enough molecules of the atmosphere would be struck by the electron and ionized to cause breakdown between those two electrodes. The presence of the normal glow discharge on the other side of electrode 20, however, keeps the atmosphere adjacent outside of the electrode at a relatively higher potential, thus discouraging the electric field from anode 12 from protruding through slots 21. This discourages long electron paths, and in effect increases the breakdown voltage to approximately twice what it would be in the absence of the glow discharge.

Thus, a simple way to fire the electronic switch is to halt the flow of electrons in the glow discharge so that the electric field can protrude further through slots 21 and furnish a long path for electrons to follow. When the discharge is halted the copious supply of electrons between electrodes and 23 is available to follow the long path and to initiate voltage breakdown between anode 12 and electrode 20 by literally shorting out the interelectrode space. The resulting voltage gradients at electrode 20 are great enough to further increase the electron supply by electrode field emission. One way of halting the electron flow is to apply a negative trigger from source 30 to electrode 22. This causes electrode 22 to replace electrode 20 as the cathode, interrupting the electron current in the region between those two electrodes, and allowing the breakdown action to occur. Examination of electrode 20 from prototypes of my invention after considerable use verifies that the initial voltage breakdown does not take place over the long path from anode 12 through slots 21 to the far side of electrode 20. Then, apparently, after sufiicient electrons have passed through the slots, the discharge transfers to the near side of electrode 20. This is verified when wave forms are observed on an oscilloscope during switching. The voltage drop in the arc is seen to decrease suddenly by about 30 volts shortly after the arc discharge is initiated, indicating a shortening of the path.

Electrode 20 is purposely made as thin as possible, usually less than the spacing between anode 12 and electrode 20, and slots 21 preferably have a fractional depth to width ratio. Thus the slots cause no constriction of electron flow, in contrast to discharge devices of the prior art'where deliberately thick slotted electrodes were used for the very purpose causing restriction and thus increasing the breakdown voltage. The result is that my invention can be made from relatively small parts in a simple manner.

One important feature of my invention is the very short delay between application of a trigger voltage and firing of the switch. This delay varies inversely with the gas pressure and is speeded up with decreasing, anode to cathode spacing. For a given voltage hold-off, since the pressure may be increased with closer spacing according to the Paschen curve, it is evident that the closest spacing practical is desirable. While the anode current is delayed a matter of only 15 nanoseconds in the early formative time, once the current really starts to build up it will rise even more rapidly. Typically with .025 inch anode-cathode spacing and a pressure of five torr helium atmosphere the anode current buildup will begin in 15 nanoseconds and will then rise to 100 amperes in l and /2 nanoseconds, as shown in FIG. 7. With a suitable circuit a 1000 ampere buildup in about 10 nanoseconds is feasible.

This delay is relatively constant over successive firings of the switch, as shown graphically in FIG. 6. Variations in delay are commonly referred to as jitter, and it is seen from the curves that with my invention it is quite possible to keep jitter below several nanoseconds even though the trigger pulses had rise times of several hundred nanoseconds. When trigger pulse rise times are reduced to a few nanoseconds, jitter is reduced to much less than one nanosecond.

The alternate embodiment shown in FIGS. 3-5 is of somewhat different construction than the preferred embodiment of FIGS. 1 and 2. Here glass body 35 is sealed to cylindrical anode 36 by a conventional glass-to-metal seal, the same seal being used wherever electrodes protrude through the glass body. Electrode 37 is seen in FIG. 4 to be perforated with round holes rather than slots, and with relatively fewer holes than electrode 38 (FIG. 5). End electrode 39 is seen to be tubulated, with a glass seal 40 at its end for sealing off after introduction of the gaseous atmosphere.

Optional circuitry with this embodiment is shown to include a source 41 of high voltage connected through resistor 42 to anode 36, and through resistor 43 to electrode 38. Load 44 is connected from ground to the anode through capacitor 45, and electrode 37 is grounded through resistor 46. With the circuitry shown, and with the spacing between anode 36 and electrode 37 determined as previously described, a normal glow discharge away from an anode will occur between electrode 38 and electrode 37. The numerous holes in electrode 38 allow the ionization to spread to some extent to the spacing between that electrode and electrode 39. However, since electrode 37 is grounded, electron flow in the adjacent interelectrode space will be away from the anode. Application of either a positive trigger on 37 or a negative trigger on electrode 38 will halt the flow of electrons in the discharge, allowing protrusion of the electric field from anode 36 through the holes in electrode 37 and furnishing a long path for electrons to initiate complete ionization and an arc discharge within the switch. Through experimentation it was found that the initial long path discharge seems to take place between anode 36 and the far end of the tubulation of electrode 39, rather than just to the far side of electrode 37 as in the previous embodiment.

If the trigger pulse amplitudes are reduced, neither the positive nor the negative trigger alone will fire the switch, but the two applied in coincidence will do so. The circuit of FIG. 3 may be changed to ground electrode 37, eliminating resistor 46. In this case the starting process is as described before, i.e., over a long path to the end of the tubulation. However, the current flowing to the anode will build up a plasma between the anode and electrode 37 and transfer conduction over a short path to the near side of electrode 37.

It is apparent from the construction shown that my invention is easily constructed and will withstand severe shocks, of the order of 100,000 times the acceleration of gravity, without damage. Because of the various novel features no special cathode material is required. Although a preferred embodiment is shown it is exemplary and may be modified without departing from the sphere and scope of my invention as defined in the claims below.

I claim as my invention:

1. An electronic switch comprising within an'envelope:

an ionizable atmosphere;

a first electrode, maintained at a highly positive potential;

a second, perforated electrode maintained at a lower potential than the first and spaced therefrom on one side;

means establishing a D.C. glow discharge on the other side of the second electrode with electron flow away from the second electrode;

and means for halting the flow of electrons, thereby initiating an arc discharge within the envelope.

2. The electronic switch of claim 1 wherein the atmospheric pressure and the interelectrode spacing are related according to the left hand side of the Paschen curve for the atmosphere.

3. The electronic switch of claim 2 wherein the firstnamed means comprises a third electrode spaced from the second electrode on its other side and maintained at a positive potential with respect thereto.

4. The electronic switch of claim 3 wherein the lastnamed means comprises:

a fourth, perforated, electrode intermediate the second and third electrodes;

and means for applying a negative voltage to said fourth electrode.

5. The electronic switch of claim 4 wherein the thicknesses of the second and fourth electrodes are individually less than the spacing between the first and second electrodes.

6. An electronic switch comprising:

means for establishing a potential difference region in an ionizable atmosphere;

means for producing an electron glow discharge adjacent to, and in a direction away from, said potential difference region;

and means causing electrical energy transfer by halting electron flow away from said potential difference region, thereby allowing electron flow into the potential difference region and ionizing said atmosphere.

7. An electronic switch comprising within an envelope:

an ionizable atmosphere;

a first electrode, maintained at a highly positive potential;

a second, radially slotted, electrode maintained at a lower potential than the first and spaced therefrom on one side;

means establishing a DC. glow discharge on the other side of the second electrode with electrode flow away from the second electrode;

and means for halting the flow of electrons, thereby initiating an arc discharge within the envelope.

8. The electronic switch of claim 7 wherein the atmospheric pressure and the interelectrode spacing are related according to the left hand side of the Paschen curve for the atmosphere.

9. The electronic switch of claim 8 wherein the firstnamed means comprises a third electrode spaced from the second electrode on its other side and maintained at a positive potential with respect thereto.

10. The electronic switch of claim 9 wherein the lastnamed means comprises:

a fourth, radially slotted, electrode intermediate the second and third electrodes;

and means for applying a negative voltage to said fourth electrode.

11. The electronic switch of claim 10 wherein the thicknesses of the second and fourth electrodes are individually less than the spacing between the first and second electrodes.

12. The method of switch electrical energy comprising the steps of:

establishing a potential difference region in an ionizable atmosphere;

producing an electron glow discharge adjacent to, and in a direction away from, said potential difference region;

and causing electrical energy transfer by halting electron fiow away from said potential difference region, thereby allowing electron flow into the potential difference region and ionizing said atmosphere.

13. An electronic switch comprising within an insulat ing envelope:

an ionizable atmosphere;

a first planar electrode at one end of the envelope maintained at a highly positive potential;

a second, perforated, planar electrode parallel to the first, spaced therefrom and maintained at a lower potential than the first;

a third planar electrode at the other end of the envelope,

parallel to the second;

a fourth, perforated, planar electrode between the sec ond and the third and parallel thereto;

means maintaining a potential difference sustaining an electron glow discharge from the second to the third electrode;

and means for driving the fourth electrode negative, halting the discharge and enabling electron flow through the perforations of the second electrode to the first, thereby initiating an arc discharge.

14. The electronic switch of claim 13 wherein the atmospheric pressure and the interelectrode spacing between the first and second electrodes are related according to the left hand side of the Paschen curve for the atmosphere.

15. The electronic switch of claim 14 wherein the thickness of the second and fourth electrodes are individually less than the spacing between the first and second electrodes.

16. The electronic switch of claim 15 wherein the second and fourth electrodes are radially slotted.

17. The electronic switch of claim 16 wherein the slots have a fractional depth-to-width ratio.

References Cited by the Examiner UNITED STATES PATENTS 2,889,481 6/ 1959 Stieritz 313-189 2,928,013 3/1960 Gawehn 313-192 3,248,603 4/1966 Howell et al 313-200 JAMES W. LAWRENCE, Primary Examiner. DAVID J. GALVIN, Examiner. R. JUDD, Assistant Examiner, 

1. AN ELECTRONIC SWITCH COMPRISING WITHIN AN ENVELOPE: AN IONIZABLE ATMOSPHERE; A FIRST ELECTRODE, MAINTAINED AT A HIGHLY POSITIVE POTENTIAL; A SECOND, PERFORATED ELECTRODE MAINTAINED AT A LOWER POTENTIAL THAN THE FIRST AND SPACED THEREFROM ON ONE SIDE; MEANS ESTABLISHING A D.C. GLOW DISCHARGE ON THE OTHER SIDE OF THE SECOND ELECTRODE WITH ELECTRON FLOW AWAY FROM THE SECOND ELECTRODE AND MEANS FOR HALTING THE FLOW OF ELECTRONS, THEREBY INITIATING AN ARC DISCHARGE WITHIN THE ENVELOPE. 